1. Field of the Invention
The present invention relates to a laminated dielectric resonator and a laminated dielectric filter for constituting a resonant circuit for use in a microwave band ranging from several hundred MHz to several GHz, and more particularly to a laminated dielectric resonator which can be manufactured with reduced variations and which enables a laminated dielectric filter, etc. to be reduced in size and manufactured with an increased yield, and a laminated dielectric filter.
2. Description of the Related Art
There has been a growing demand for small-size and lower-loss laminated dielectric filters in view of a wide variety of radio communication systems such as portable telephone sets available in the art.
Smaller sizes of laminated dielectric filters can be achieved by reducing the size of resonators (resonant electrodes) used therein.
For reducing the size of a resonator, it has been customary to add a capacitance to an open end of a resonant electrode. For example, as shown in FIG. 10 of the accompanying drawings, a laminated dielectric filter 200 has a resonant electrode 206 formed in a dielectric substrate 204 with a ground electrode 202 disposed on its surfaces, and a plurality of inner-layer ground electrodes 208, 210 formed in the dielectric substrate 204. The inner-layer ground electrodes 208, 210 sandwich an open end 206a of the resonant electrode 206.
Because of the inner-layer ground electrodes 208, 210 that overlap a portion of the open end of the resonant electrode 206 with a dielectric layer interposed therebetween, the impedance of the resonator or resonant electrode 206 is changed to make the resonator smaller in size. As the size of the resonator is smaller, however, the area in which the inner-layer ground electrodes 208, 210 overlap the portion of the open end of the resonant electrode 206 is smaller. Therefore, in order to lower the impedance of the resonator, or particularly the impedance of the open end thereof, it is necessary to reduce the thickness of the dielectric layer interposed between the resonant electrode 206 and the inner-layer ground electrodes 208, 210.
With the overlapping area being smaller, however, if the inner-layer ground electrodes 208, 210 are misaligned with each other in overlapping relation to the resonant electrode 206, the capacitance between the resonant electrode 206 and the inner-layer ground electrodes 208, 210 is greatly changed. Such capacitance changes tend to cause variations in dimensions of laminated dielectric filters that are manufactured, resulting in characteristic variations thereof.
It is therefore an object of the present invention to provide a laminated dielectric resonator and a laminated dielectric filter which are designed to suppress characteristic variations due to a misalignment between inner-layer ground electrodes in overlapping relation to a resonant electrode, and also to enable the laminated dielectric filter, etc. to be manufactured with an increased yield.
According to the present invention, a laminated dielectric resonator comprises a dielectric substrate comprising a plurality of laminated dielectric layers and an inner-layer ground electrode and a resonant electrode which are disposed in the dielectric substrate. The dielectric substrate includes a portion in an overlapping region where an open end portion of the resonant electrode and the inner-layer ground electrode overlap each other. The portion has a dielectric constant higher than another portion of the dielectric substrate.
The value of capacitance between the resonant electrode and the inner-layer ground electrode is governed by the portion in the overlapping region where the open end portion of the resonant electrode and the inner-layer ground electrode overlap each other. Therefore, even if the inner-layer ground electrode is misaligned in overlapping relation to the resonant electrode, only the overlapping area of the portion having a lower dielectric constant is changed. Therefore, any change in the value of capacitance between the resonant electrode and the inner-layer ground electrode is small.
With the laminated dielectric resonator according to the present invention, characteristic variations due to a misalignment of the inner-layer ground electrode in overlapping relation to the resonant electrode are suppressed, and the laminated dielectric filter, etc. can be manufactured with an increased yield.
In the above laminated dielectric resonator, a space may be defined in the portion of the dielectric substrate in the overlapping region and filled with a member having a dielectric constant higher than the dielectric layer interposed between the resonant electrode and the inner-layer ground electrode.
The above space which is filled with the above member is highly effective in producing the above arrangement in which the dielectric constant of the portion in the overlapping region where the open end portion of the resonant electrode and the inner-layer ground electrode overlap each other is higher than the other portion of the dielectric substrate.
The member may have an end held in contact with or close to the resonant electrode and an opposite end held in contact with or close to the inner-layer ground electrode.
According to the present invention, a laminated dielectric filter comprises a dielectric substrate comprising a plurality of laminated dielectric layers and a resonant electrode and another electrode which are disposed in the dielectric substrate. The dielectric substrate includes a portion in an overlapping region where an open end portion of the resonant electrode and the other electrode overlap each other. The portion has a dielectric constant higher than another portion of the dielectric substrate.
Accordingly, characteristic variations due to a misalignment of the inner-layer ground electrode in overlapping relation to the resonant electrode are suppressed, and the laminated dielectric filter can be manufactured with an increased yield.
In the laminated dielectric filter, the other electrode may comprise an inner-layer ground electrode. The resonant electrode may comprise a plurality of resonant electrodes. The other electrode may comprise a coupling adjusting electrode disposed in the dielectric substrate for adjusting the coupling between the resonant electrodes.
Alternatively, the resonant electrode may comprise a plurality of resonant electrodes. The other electrode may comprise either one or both of an input electrode and an output electrode. The input electrode may be disposed in the dielectric substrate and capacitively couple one of the resonant electrodes which serves as an input resonant electrode to an input terminal. The output electrode may be disposed in the dielectric substrate and capacitively couple the other of the resonant electrodes which serves as an output resonant electrode to an output terminal.